Thay đổi giao diện Admin WordPress 5.3 về giao diện cũ.

admin.min.css

input[type=text]{border:1px solid #ddd;box-shadow:inset 0 1px 2px rgba(0,0,0,.07);background-color:#fff;color:#32373c;outline:0;transition:50ms border-color ease-in-out}input[type=text]:focus{border-color:#5b9dd9;box-shadow:0 0 2px rgba(30,140,190,.8);outline:2px solid transparent}textarea{border:1px solid #ddd;box-shadow:inset 0 1px 2px rgba(0,0,0,.07);background-color:#fff;color:#32373c;outline:0;transition:50ms border-color ease-in-out}textarea:focus{border-color:#5b9dd9;box-shadow:0 0 2px rgba(30,140,190,.8);outline:2px solid transparent}select{padding:2px;line-height:28px;height:28px;vertical-align:middle;border:1px solid #ddd;box-shadow:inset 0 1px 2px rgba(0,0,0,.07);background-color:#fff;color:#32373c;outline:0;transition:50ms border-color ease-in-out}select:focus{border-color:#5b9dd9;box-shadow:0 0 2px rgba(30,140,190,.8);outline:2px solid transparent}input[type=radio]{border:1px solid #b4b9be;border-radius:50%;background:#fff;color:#555;clear:none;cursor:pointer;display:inline-block;line-height:0;height:16px;margin:-4px 4px 0 0;outline:0;padding:0!important;text-align:center;vertical-align:middle;width:16px;min-width:16px;-webkit-appearance:none;box-shadow:inset 0 1px 2px rgba(0,0,0,.1);transition:.05s border-color ease-in-out}input[type=radio]:checked:before{content:"\2022";text-indent:-9999px;border-radius:50px;font-size:24px;width:6px;height:6px;margin:4px;line-height:16px;background-color:#1e8cbe}input[type=checkbox]{border:1px solid #b4b9be;background:#fff;color:#555;clear:none;cursor:pointer;display:inline-block;line-height:0;height:16px;margin:-4px 4px 0 0;outline:0;padding:0!important;text-align:center;vertical-align:middle;width:16px;min-width:16px;-webkit-appearance:none;box-shadow:inset 0 1px 2px rgba(0,0,0,.1);transition:.05s border-color ease-in-out}.wp-core-ui .button,.wp-core-ui .button-primary,.wp-core-ui .button-secondary{display:inline-block;text-decoration:none;font-size:13px;line-height:26px;height:28px;margin:0;padding:0 10px 1px;cursor:pointer;border-width:1px;border-style:solid;-webkit-appearance:none;border-radius:3px;white-space:nowrap;box-sizing:border-box}.wp-core-ui .button-primary{background:#0085ba;border-color:#0073aa #006799 #006799;box-shadow:0 1px 0 #006799;color:#fff;text-decoration:none}.wp-core-ui .button-primary.focus,.wp-core-ui .button-primary.hover,.wp-core-ui .button-primary:focus,.wp-core-ui .button-primary:hover{background:#008ec2;border-color:#006799;color:#fff}.wp-core-ui .button-primary.focus,.wp-core-ui .button-primary:focus{box-shadow:0 1px 0 #0073aa,0 0 2px 1px #33b3db}.wp-core-ui .button,.wp-core-ui .button-secondary{color:#555;border-color:#ccc;background:#f7f7f7;box-shadow:0 1px 0 #ccc;vertical-align:top}.wp-core-ui .button-secondary:focus,.wp-core-ui .button-secondary:hover,.wp-core-ui .button.focus,.wp-core-ui .button.hover,.wp-core-ui .button:focus,.wp-core-ui .button:hover{background:#fafafa;border-color:#999;color:#23282d}.wp-core-ui .button-secondary:focus,.wp-core-ui .button.focus,.wp-core-ui .button:focus{border-color:#5b9dd9;box-shadow:0 0 3px rgba(0,115,170,.8)}.wp-admin select,input[type=color],input[type=date],input[type=datetime-local],input[type=datetime],input[type=email],input[type=month],input[type=number],input[type=password],input[type=search],input[type=tel],input[type=text],input[type=time],input[type=url],input[type=week],select,textarea{border:1px solid #ddd;box-shadow:inset 0 1px 2px rgba(0,0,0,.07);background-color:#fff;color:#32373c;outline:0;transition:50ms border-color ease-in-out}.widefat thead td,.widefat thead th{border-bottom:1px solid #e1e1e1}.wrap .add-new-h2:hover,.wrap .page-title-action:hover{border-color:#008ec2;background:#00a0d2;color:#fff}.page-title-action:focus{color:#124964}.wrap .page-title-action:focus{border-color:#5b9dd9;box-shadow:0 0 2px rgba(30,140,190,.8);outline:2px solid transparent}.wrap h1.long-header{padding-right:0}.wp-dialog{background-color:#fff}#available-widgets .widget-top:hover,#widgets-left .widget-in-question .widget-top,#widgets-left .widget-top:hover,.widgets-chooser ul,div#widgets-right .widget-top:hover{border-color:#999;box-shadow:0 1px 2px rgba(0,0,0,.1)}.wrap .add-new-h2,.wrap .add-new-h2:active,.wrap .page-title-action,.wrap .page-title-action:active{margin-left:4px;padding:4px 8px;position:relative;top:-3px;text-decoration:none;border:none;border:1px solid #ccc;border-radius:2px;background:#f7f7f7;text-shadow:none;font-weight:600;font-size:13px;line-height:normal;color:#0073aa;cursor:pointer}.postbox{position:relative;min-width:255px;border:1px solid #e5e5e5;box-shadow:0 1px 1px rgba(0,0,0,.04);background:#fff}.postbox .hndle,.stuffbox .hndle{border-bottom:1px solid #eee}