Hi @frosticek,
Changes were made to the style.css file and it shows the box width was expanded but the module box is not and the height is higher.
This is my code under LOGIN & REGISTER form; thanks in advance.
/* LOGIN & REGISTER FORM */
#i-forms .box {max-width:600px!important;}
#i-forms {float:left;width:100%;text-align:center;clear:both;margin-bottom:70px;font-size:13px;line-height:16px;}
#i-forms h2 {font-size:20px;font-weight:normal;color:#fff;margin:10px 0 10px 0;font-weight:600;line-height:20px;}
#i-forms fieldset {width:100%;float:left;clear:both;}
#i-forms .external-log {float:left;width:100%;clear:both;color:#fff;font-size:12px;line-height:14px;font-weight:bold;text-align:center;margin:0 0 10px 0;color:#fff;padding:12px 10px;}
#i-forms .external-log i {float:left;line-height:14px;font-size:20px;}
#i-forms .external-log.fb {background:#3b5998;border-color:#3b5998;}
#i-forms .external-log.fb:hover {background:#5477bf;}
#i-forms .external-log.gc {background:#dd4b39;border-color:#dd4b39}
#i-forms .external-log.gc:hover {background:#e67263;}
#i-forms #right #recaptcha_widget_div {width:100%;margin:20px 0;background:#f0f0f0;color:#777;padding:15px 0;clear:both;float:left;}
#i-forms #right #recaptcha_area, #i-forms #right #recaptcha_table {margin:0 0 0 30%;}
#i-forms .req-what {text-align:left;margin-top:-15px;display:none!important;}
#i-forms .box {width:100%;max-width:360px;display:inline-block;margin:0 auto;}
#i-forms .box .user_forms {padding:25px;background:rgba(255,255,255,0.95);border:4px solid #ddd;}
#i-forms form label {float:left;width:100%;clear:both;color:#333;margin:0 0 5px 0;text-align:left;}
#i-forms form .input-box-check {width:auto;margin:0;}
#i-forms form .input-box-check label {cursor:pointer;font-size:12px;font-weight:600;line-height:21px;}
#i-forms form .input-box-check label:hover {text-decoration:underline;}
#i-forms .input-box {float:left;width:100%;clear:both;margin:0 0 25px 0;position:relative;}
#i-forms .input-box input:not([type="radio"]):not([type="checkbox"]):not([type="file"]):not([type="submit"]), #i-forms .input-box select {float:left;width:100%;clear:both;margin:0;padding-left:28px;}
#i-forms .input-box i {position:absolute;font-size:16px;font-weight:500;color:#111;top:11px;left: 2px;width:26px;text-align:center;line-height:16px;}
#i-forms .input-box.last {margin-bottom:5px;}
#i-forms button {margin-top: 15px; font-size: 13px; font-weight: bold; width: 100%;}
#i-forms .swap {float:left;width:100%;clear:both;padding:15px 0 0 0;margin:20px 0 0 0;border-top:1px solid #eee;}
#i-forms .swap a {color:#000;text-transform:uppercase;font-weight:600;text-decoration:none;}
#i-forms .swap a:hover {text-decoration:underline;}
#i-forms .or {float:left;width:100%;clear:both;position:relative;font-size:13px;color:#999;text-align:center;line-height:16px;height:16px;margin:18px 0 20px 0;}
#i-forms .or > div.left {position:absolute;width:40%;top:9px;left:0;z-index:1;border-top:1px solid #eee;}
#i-forms .or > div.right {position:absolute;width:40%;top:9px;right:0;z-index:1;border-top:1px solid #eee;}
#i-forms .or > span {display:inline-block;line-height:16px;}
See attached image.